Segments - Net sales by major geographic area (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2019 USD ($) $ / $	Jan. 31, 2018 USD ($) $ / $	Jan. 31, 2019 USD ($) $ / $	Jan. 31, 2018 USD ($) $ / $
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	$ 723,902	$ 585,508	$ 2,335,883	$ 1,875,669
Average exchange rates | $ / $	0.7491	0.7895	0.7609	0.7875
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	$ 624,672	$ 585,508	$ 2,021,750	$ 1,875,669
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	$ 99,230		$ 314,133